Answering that question with a reasonable degree of accuracy proved nettlesome in days past, though some primitive pregnancy tests had genuine scientific merit.

Ancient Egypt

One of the first known ways of detecting a pregnancy comes from an ancient Egyptian document estimated to be from 1350 B.C. [11 Big Fat Pregnancy Myths]

The papyrus document suggests a woman urinate on wheat and barley seeds. If the wheat sprouted, a female child was on its way, the ancients decreed, and if the barley sprouted, a male child would soon arrive. No sprouts meant no child was expected.

Strangely, researchers in the 1960s tested this method and found it had a grain of truth, according to the National Institutes of Health. Higher-than-normal levels of estrogen in pregnant women's urine, scientists speculated, may stimulate the germination of seeds (but were useless at predicting the sex of the child).

Middle Ages

A woman's urine was used as a way to determine her pregnancy status during the Middle Ages, too, when so-called "piss prophets" believed that if a needle placed in a vial of urine turned rust red or black, the woman was probably pregnant, io9.com reports.

Another popular test involved mixing wine with urine and watching the resulting changes. Since alcohol can react with the proteins in urine, this test might have been successful if analyzed by someone who knew what color-related changes to look for.

Some 17th-century doctors dipped a ribbon into a pot of a woman's urine; if the smell of the ribbon made the woman gag or feel nauseous, she was presumed pregnant, mentalfloss.com reports.

The 1920s to 1960s

Before the 1920s, there were virtually no advances in pregnancy tests, most of which relied on old wives' tales and other hokum.

But in the 1920s, medical researchers were able to identify a hormone, human chorionic gonadotropin or hCG, that's found only in pregnant women, marking the first time a single compound was discovered that could indicate pregnancy status.

To determine the presence of hCG, a sample of the woman's urine was injected into an immature female mouse, frog or rabbit. If hCG was present in the urine sample, the animal would go into heat, indicating the woman was pregnant.

The test, known as the Aschheim-Zondek test (after its developers), the A-Z test or the "rabbit test," was about 98 percent accurate. Women would euphemistically claim "the rabbit died" when referring to their pregnancy.

Testing involving frogs took a bizarre turn in the 1940s when thousands of African clawed frogs were imported for pregnancy testing. A few escaped, carrying with them a fungus, Batrachochytrium dendrobatidis, that's blamed for a massive die-off of native North American frogs and other amphibians.

The "rabbit test" and other tests like it weren't fool-proof: Not only were they expensive and time-consuming (results could take days to arrive), but the test couldn't always distinguish between hCG and luteinizing hormone, and certain medications could yield a false-positive or false-negative result.

The 1970s

When the sexual revolution arrived, medical science was ready: In 1972, scientists reported for the first time a radioimmunoassay pregnancy test that could distinguish between hCG and luteinizing hormone in a woman's urine.

In 1976, drug maker Warner-Chilcott sought approval from the Food and Drug Administration (FDA) for an early-pregnancy test, or "e.p.t." For $10, women could purchase the two-hour test kit to use in the privacy of her own home; it included a vial of purified water, an eye dropper, a test tube and an assortment of compounds including sheep's blood.

Used correctly, the e.p.t. was 97 percent accurate for positive results and 80 percent accurate for negative results.

The 1990s to today

As testing methods continued to improve, researchers found that enzyme indicators on home pregnancy test strips could replace radioactive labels. Other modern conveniences include results within a few minutes and a digital display to replace the thin line indicating pregnancy.

Modern pregnancy tests — which still rely on the presence of hCG in urine — are up to 99 percent accurate, depending on the presence of certain medications, following the test's instructions accurately and how soon after pregnancy the test is performed. (The makers of e.p.t., which now stands for "error-proof testing," recommend waiting at least a week after a missed period.)

Marc Lallanilla has been a science writer and health editor at About.com and a producer with ABCNews.com. His freelance writing has appeared in the Los Angeles Times and TheWeek.com. Marc has a Master's degree in environmental planning from the University of California, Berkeley, and an undergraduate degree from the University of Texas at Austin.